A proposal offered by Iran during talks in Geneva over concerns with its nuclear program contained “a level of seriousness and substance that we had not seen before,” the White House says.

White House Spokesman Jay Carney said Wednesday that “no one should expect a breakthrough overnight,” but called Iran’s proposal “useful,” according to Reuters.

The comments came as Iran concluded two days of meetings with officials from the United States, Russia, China, Britain, France and Germany at the U.N.’s offices in Geneva.

The countries arranged the talks because they suspect Iran is using its nuclear facilities to build weapons, while Iran denies those claims.

Iran, hoping to end the confrontation over its nuclear program, introduced the three-stage proposal to the countries during a PowerPoint presentation on Tuesday morning.

Details on the proposal have remained sparse, but a member of one of the delegations at the talks told the Associated Press that the new Iranian plan offered reductions in both the levels of uranium enrichment being conducted by Iran and the number of centrifuges doing the enrichment – a key demand of the six powers.

An Iranian official also reportedly suggested Wednesday that Tehran is ready to address concerns about the level of access that International Atomic Energy Agency inspectors get inside the country.